The present invention relates generally to dovetail slots formed in disks of a gas turbine engine and, in particular, to an apparatus and method for inspecting such dovetail slots to ensure the proper width between adjacent parallel slot portions thereof.
It will be understood that gas turbine engines include compressors and turbines which include a plurality of circumferentially spaced blades connected to and extending from a disk. Typically, the blades are held in the disk by machining multiple slots around the perimeter of the disk and sliding the blade, which has a similarly shaped feature at its base, into the slot. The machined slots are oftentimes called dovetail slots because of their shape and must be held to close tolerances. One particular parameter which must be measured is the slot width, defined herein as the distance between a pair of pin members seated within adjacent parallel slot portions of the dovetail slot.
The dovetail slot width parameter is important because the respective bearing surfaces of the slot portions are crucial in maintaining the blade within the dovetail slot and incur the greatest amount of stress. It will be appreciated that the dovetail slot is generally formed by means of a broaching process, wherein the dovetail slot is progressively formed to a desired shape and dimension by a corresponding device. When the broaching device exhibits wear, the dovetail slot will not be formed in an exact manner. Accordingly, inspecting and monitoring the slot width of the dovetail slot enables broach wear to be recognized so that the device can be repaired or replaced.
Currently, a pair of precision gage pins are manually positioned in the slot portions and the distance between inner tangent points of such pins are measured. This requires a technician to hold the gage pins in one hand while simultaneously forcing a gage block between them using the other hand. If the gage block chosen is not the correct size, the technician must choose another gage block from the set and attempt to fit it between the gage pins. This process iterates until the best fitting gage block is found. Once the best gage block is obtained, the technician must hold the gage pins, as well as the gage block, in one hand and slide shims between the gage block and one of the gage pins until a precise fit is obtained between the gage pins. The thickness of the gage block and the shims is then added together to determine the slot width. This process generally takes approximately one-two minutes for each dovetail slot. Since a disk may have over 100 slots formed in its periphery, the time required to measure the slot width for all such dovetail slots therein could take several hours.
Accordingly, it would be desirable for an apparatus and method to be developed which inspects dovetail slot width in a quicker and more reliable manner. It is also desirable for such apparatus to be user friendly and able to be integrated in a system to monitor and control the manufacturing of such dovetail slots.
In a first exemplary embodiment of the invention, an apparatus for inspecting a dovetail slot of a gas turbine engine disk is disclosed as including: a first pin member fixed in a stationary position; a second pin member having the ability to move between a first position and a second position, wherein the second pin member is oriented substantially parallel to the first pin member; a member actuable between a first position and a second position, wherein the member functions to automatically position the first and second pin members in a predetermined position within the dovetail slot when in the second member position; a first probe for measuring a distance between the first and second pin members when in the predetermined dovetail slot position; and, at least one plate member forming a base to which the first pin member, the second pin member, the actuable member, and the first probe are assembled in a predetermined manner.
In a second exemplary embodiment of the invention, a method of inspecting a dovetail slot for a gas turbine engine disk is disclosed as including the following steps: positioning a stationary pin member and a movable pin member within the dovetail slot; actuating a member from a first position to a second position so as to interface with the movable pin member until the stationary and movable pin members are automatically seated in a pair of substantially parallel slots within said dovetail slot; and, measuring a distance between the fixed and movable pin members when in the seated position.
In accordance with a third embodiment of the invention, an apparatus for inspecting a dovetail of a gas turbine engine blade is disclosed as including: a first pin member fixed in a stationary position; a second pin member having the ability to move between a first position and a second position, wherein the second pin member is oriented substantially parallel to the first pin member; a member actuable between a first position and a second position, wherein the member functions to automatically position the first and second pin members in a predetermined position on opposing sides of the dovetail during the second member position; a first probe for measuring a distance between the first and second pin members when in the predetermined position; and, at least one plate member forming a base to which the first pin member, the second pin member, the actuable member, and the first probe are assembled in a predetermined manner.